"I never look back, darling. It distracts from the now."-Edna Mode (The Incredibles)

If you're constantly bringing up the past, you're not fully focused on the present. The past already happened and you can't change it, so there is no use in dwelling on it. Edna Mode has the right idea in focusing on the present rather than living in the past.

Source: Mode, Edna. The Incredibles, 2004. Web. May 14, 2012